Electroencephalography (EEG) is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain. It is desirable to determine the source of certain electrical activity that is discernable from the EEG. For example, EEGs are utilized as part of diagnosis and surgical treatment planning for patients that may suffer from focal epilepsy. The process of finding the location and distribution of the sources that create these activities is called electrical source imaging (ESI) or source localization. However, existing source localization methods using EEG tend to be overly complicated for the user when accurate estimates are required.
Magnetoencephalography (MEG) is a technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain. MEG can be used for source localization, such by calculating a set of equivalent current dipoles. While MEG may often provide increased accuracy relative EEG, the underlying technology is much more expensive and not as readily available.